Weft yarn feeding devices used in modern power looms (jet looms, gripper looms, projectile looms, or other types) frequently are autonomic units controlling the speed of the drive motor of the winding element essentially independent from the weaving operation in the power loom and exclusively in dependence from the permanently detected size of the yarn store in the feeding device. The yarn store is permanently detected in order to generate control signals for the control device of the feeding device which control device switches on or switches off the drive motor or accelerates or decelerates the drive motor, in order to maintain a size of the yarn store sufficient to cover the consumption. In case that a yarn consumption results in a decrease of the size of the yarn store in relation to a predetermined reference size, then the drive motor either is switched on and accelerated or is only accelerated until the reference size at least partially is reached again. In case that the size of the yarn store increases in relation to the reference size, then the drive motor is decelerated or is switched off. The yarn store in the feeding device is monitored by sensors. The drive motor operates with a predetermined acceleration behaviour. Depending on the case of application of the feeding device a predetermined maximum speed may be set for the drive motor.
According EP 0 114 339 B, a common control device is provided for several weft yarn measuring feeding devices in a jet power loom. The common control device, depending on the weaving pattern, selects and controls only one feeding device. As all measuring feeding devices include yarn stop devices, a control routine is implemented using a preparation switch by which the yarn store is brought in each measuring feeding device to a maximum size prior to the start-up of the power loom. For this function, the drive motor is driven for a sufficiently long time period and then is stopped again. The normal control routine depending from the size of the yarn store is set out of function for the preparation phase. Furthermore, a start-up switch is provided in the power loom and upon actuation starts the weaving operation. The actuation of the start-up switch signals the control device of the measuring feeding devices so that each one will again operate with a control routine depending on the yarn store size detection. The stopping devices are brought into their respective release position in timed fashion and one by one by respective trig or trigger signals transmitted from the power loom. As soon as an under-sized yarn consumption is detected, the yarn store size monitoring device of the respective measuring feeding device responds and generates control signals to start the drive motor in order to replenish the yarn store. There is an unavoidable time delay between the start-up of the weaving operation in the power loom and the acceleration of the drive motor as controlled by the control device. Since the power loom rapidly reaches its full load operation and causes high start-up yarn consumption, the yarn store in the actuated measuring feeding device may be emptied, resulting in an operation disturbance.
A rapidly operating power loom equipped with one feeding device only, e.g. a water jet power loom, for processing a single weft yarn quality only causes upon start-up of the weaving operation extremely rapid high start-up yarn consumption possibly causing a quickly emptied yarn store due to the time delay between the start of the weaving operation or the occurrence of the run-signal, respectively, and the response of the drive motor of the feeding device depending on the initial yarn store size. This is not only true for power looms equipped with several measuring feeding devices or with one measuring feeding device only, but also for power looms being equipped with another type of a feeding device and/or with several feeding devices, in the case that the power loom produces a rapidly starting and strong start-up yarn consumption. This drawback can be avoided by extremely powerful and strongly accelerating drive motors of the feeding devices, i.e. by expensive special feeding devices. Such special feeding devices, however, generate undesirably high load for the respective yarn.
It is known in practice for measuring feeding devices used in fast jet weaving machines to switch on and to accelerate the drive motor after or in synchronism with the occurrence of the first trig signal output for the stop device and as transmitted after startup of the weaving operation of the power loom. However, since then the drive motor only starts at the same moment as the trig signal is transmitted or even later, in some cases there will not be sufficient yarn in the yarn store in order to cover the high start-up yarn consumption.
It is an object of the invention to provide a method of the kind as disclosed and a yarn processing system allowing to avoid an emptying of the yarn store in the feeding device despite a strong and rapidly increasing start-up yarn consumption by the weaving machine, and to achieve that function by commercial available feeding devices and in a structural simple way.